Oil Tank / Cam Cover Breathers

Does anyone know what the function of the two hoses that go from the front cylinder cam covers to the oil tank is?
Is there any reason I shouldn't vent them to the atmosphere?
Is there any good reason I shouldn't use these cam cover breathers, fit two like it to the rear cylinder and vent them to the atmosphere as well?
Being bad for squirrels is not, IMO, a valid reason.

Just ordered 3 breather sets from Redline Motorcycles.
£40 or thereabouts.
Had to buy 3 sets because one of mine got fubar in transit from Bob Farnham's.

They are there as the oil pump that sends oil back to the tank can also send air with it. WIthout these the tank would become pressurised. They return air back to the front cylinder where it travels down cam chain area and back into crank. Well thats according to http://www.ktm950.info/

I noticed today that the rear cover is a twin of the front and has everything there to fit the breathers. I'm going to order up the parts but are 2 really necessary on the rear? I was thinking of letting the oil tank vent to atmosphere and also the 2 front cam breathers with one rear.

Just replaced battery on the OE SDR and topped up oil at same time - had air hiss as oil filler cap was unscrewed but not sure whether tank was positively or negatively pressurised - not come across this before and would be suprised if both front cylinder vent pipes are blocked - blocked/stuck crankcase breather valve? Any other thoughts?